The characteristics of GaN epitaxial layers grown on Si(1 1 1) with a low-temperature AlN interlayer have been investigated, when the thickness of the 1st GaN layer is varied. The thickness of the 1st GaN layer reduces the stress sufficiently to avoid crack formations in the GaN layers; further, the existence of an optimal thickness has been shown. Lower thicknesses result in heavy cracking as a result of strong tensile stresses, while higher thicknesses lead to the saturation of crack density. Further, it is confirmed that the formation of a crack or threading dislocation as the dominant factor for relaxing strain is dependent on the thickness of the 1st GaN layer. The 1st GaN layer plays a key role in ensuring that a GaN layer with a low-temperature AlN interlayer has no cracks. (C) 2009 Elsevier B.V. All rights reserved.